Many computer systems include disk-drive memory systems to store data, such as hard-disk drives (HDD) and/or peripheral disk-drive systems. The disk-drives can incorporate a spindle motor that can be configured as a servo motor. To provide proper function of the disk-drive system, such as for auto-start procedures, it can be necessary to monitor a rotational speed of the disk-drive spindle motor, such as by measuring a back electromagnetic force (BEMF) of the servo motor for a given phase of the servo motor. The BEMF of the servo motor can be proportional to the rotational speed of the servo motor, such that a servo motor control scheme can be properly adjusted to maintain the rotational speed of the servo motor at a desired rate of rotation.